The present invention relates generally to a method and to an optical arrangement in an optical network, and more specifically to a method and to an arrangement for achieving tunable optical transmission or reception on optical wavelength channels.
A number of different methods of further increasing the capacity of existing optical networks are known to the art. One way is to use so-called wavelength multiplexing (WDM) techniques for improving the extent to which available bandwidths can be utilised on an optical fibre in an optical network. The wavelength can also be used in an optical network as address information, i.e. the information can be multiplexed on a number of channels that can then be processed individually in the network.
This requires components that are functional in multiplexing/demultiplexing transmission channels that lie on different carrier wave lengths. It may also be desirable to change the transmitter wavelength of a given transmitter (laser). A component such as a wavelength selecting transmitter can then be used.
The drawbacks with known techniques capable of achieving wavelength selective transmission or WDM reception is that they are often complex, expensive and difficult to implement. A primary difficulty resides in tuning over a wide frequency range with the aid of solely one single laser.
Any one of a number of different known methods can be used to increase the capacity of an optical transmission system. For instance, in the case of wavelength multiplexing, transmission channels are multiplexed and demultiplexed on different carrier wave lengths to and from an information stream. These multiplexing and demultiplexing processes require the presence of optical wavelength selective devices. In order to change the transmission wavelength of a given transmitter, such devices as wavelength selecting transmitters are necessary.
An object of the present invention is to reduce the complexity and lower the costs of a wavelength selecting transmitter or a WDM receiver (Wavelength Division Multiplexing).
This is achieved in accordance with the invention with a wavelength selecting transmitter that includes two Nxc3x97N MMI waveguides, where Nxe2x89xa72, 2(Nxe2x88x921) lasers and N-number of Mach-Zehnder waveguides. A first Nxc3x97N MMI waveguide is arranged with Nxe2x88x921 number of lasers and a free access waveguide on a first side, and N-number of Mach-Zehnder waveguides of different lengths on a second side. The free access waveguide is coupled with a last port on the first side of the first MMI waveguide. A second Nxc3x97N MMI waveguide is coupled with said N-number of Mach-Zehnder waveguides on a second side and the Nxe2x88x921 number of lasers and an access waveguide on a first side, where at least one Mach-Zehnder waveguide can include at least one trimming section. The free access waveguides is coupled with a first port on the first side of the second MMI waveguide. A first to a last Mach-Zehnder waveguide are disposed between a first to a last port on a second side of the first MMI waveguide and a last to a first port on a second side of the second MMI waveguide.
In a preferred embodiment of the inventive wavelength selecting transmitter, all of the Nxe2x88x921 number of lasers coupled with the first Nxc3x97N MMI waveguide transmit with different light wavelengths, these wavelengths being the same wavelengths as those transmitted by the Nxe2x88x921 number of different lasers coupled with the second Nxc3x97N MMI waveguide.
In another preferred embodiment of the inventive wavelength selecting transmitter, an external modulator is coupled with the free access waveguides disposed on the first and on the second MMI waveguide.
In a first embodiment of a WDM receiver, the receiver includes two Nxc3x97N MMI waveguides, where Nxe2x89xa72, two access waveguides for incoming wavelength channels, 2(Nxe2x88x921) number of access waveguides for outgoing wavelength channels, and N-number of Mach-Zehnder waveguides of mutually different lengths. A first Nxc3x97N MMI waveguide is arranged with a first access waveguide to a last port of the first side of incoming wavelength channels which are provided with means for transmitting on at least one wavelength channel and Nxe2x88x921 number of access waveguides for outgoing wavelength channels on a first side and N-number of Mach-Zehnder waveguides on a second side. A second Nxc3x97N MMI waveguide is arranged with said N-number of Mach-Zehnder waveguides on a second side and a second access waveguide for incoming wavelength channels coupled with a first port on a first side which is coupled with means for transmitting at least one wavelength channel and Nxe2x88x921 number of access waveguides for outgoing wavelength channels on the remaining ports on said first side. At least one Mach-Zehnder waveguide can include at least one trimming section. A first to a last Mach-Zehnder waveguide are disposed between a first to a last port on the second side of the first MMI waveguide and a last to a first port on the second side of the second MMI waveguide.
In a preferred embodiment of the inventive WDM receiver, said receiver includes transmitter means which includes a multiplexer with which at least one laser is coupled.
According to another preferred embodiment of the inventive WDM receiver, wavelengths are transmitted from the first MMI waveguide that are different to the wavelength channels transmitted from the second MMI waveguide.
According to a further preferred embodiment of the inventive WDM receiver, there is transmitted from the first MMI waveguide at least one wavelength channel which is the same as at least one wavelength channel transmitted from the second MMI waveguide.
In a method for wavelength selection or WDM transmission, there is transmitted q of Nxe2x88x921 number of wavelength channels to q of Nxe2x88x921 number of access waveguides for incoming wavelength channels disposed on a first side of a first Nxc3x97N MMI waveguide, where Nxe2x89xa72 and where 1xe2x89xa6qxe2x89xa6Nxe2x88x921. Nxe2x88x921 number of wavelength channels are transmitted to Nxe2x88x921 number of access waveguides for incoming wavelength channels disposed on a first side of a second Nxc3x97N MMI waveguide, where Nxe2x89xa72. The wavelength channels are then transmitted through said first and said second Nxc3x97N MMI waveguides. The wavelength channels are excited into N-number of Mach-Zehnder waveguides of mutually different lengths disposed on a second side of the first and the second Nxc3x97N MMI waveguides. It is possible to change the phase of said wavelength channels in at least one Mach-Zehnder waveguide, by means of at least one trimming section disposed in a Mach-Zehnder waveguide. Said wavelength channels are then excited into the second side of the first and the second Nxc3x97N MMI waveguides and are then transmitted through the first and the second Nxc3x97N MMI waveguides and thereafter excited out on a first access waveguide for outgoing wavelength channels on the first side of the first Nxc3x97N MMI waveguide and a second access and waveguide for outgoing wavelength channels on the first side of the second Nxc3x97N MMI waveguide.
According to one WDM receiving method, Nxe2x88x921 number of wavelength channels are transmitted to an access waveguide for incoming wavelength channels disposed on a first side of a first Nxc3x97N MMI waveguide, where Nxe2x89xa72. Nxe2x88x921 number of wavelength channels are transmitted to an access waveguide for incoming wavelength channels disposed on a first side of a second Nxc3x97N MMI waveguide, where Nxe2x89xa72. Said wavelength channels are transmitted through said first and said second Nxc3x97N MMI waveguides. Said wavelength channels are excited into N-number of Mach-Zehnder waveguides of mutually different lengths disposed on a second side of the first and second Nxc3x97N MMI waveguides. The phase of said wavelength channels can be changed by at least on trimming section in at least one Mach-Zehnder waveguide. Said wavelength channels are excited into the second side of the first and the second Nxc3x97N MMI waveguides. Said wavelength channels are transmitted through the first and the second Nxc3x97N MMI waveguide and thereafter excited out on Nxe2x88x921 number of access waveguides for outgoing wavelength channels disposed on the first side of the first Nxc3x97N MMI waveguide and on Nxe2x88x921 number of access waveguides for outgoing wavelength channels disposed on the first side of the second Nxc3x97N MMI waveguide.
The object of the present invention is to obtain a wavelength selecting transmitter module or receiver module that work in pairs and therewith require only one in-trimming.
One advantage afforded by the present invention is that the arrangement can transmit and receive carrier wavelengths simultaneously on the same or on different wavelengths which require only one in-trimming.
The invention will now be described in more detail with reference to preferred embodiments thereof and with reference to the accompanying drawings.